Segment linkage and the state of stress in transtensional transfer zones: field examples from the Pannonian Basin

Abstract

Abstract Metre- to kilometre-scale en échelon strike-slip faults were mapped at the 1:10 000 scale in the Gánt mining area of the Vértes Hills in central Hungary. Good exposures allow detailed observation of brittle structures within the transfer zones of the overstepping fault segments. The strike-slip segments are subvertical to steeply dipping, with a rake of 20–30° accommodating a noticeable dip-slip. Displacement transfer between strike-slip faults was achieved through transtensional relay ramps, which represent a specific type of transfer zone. The breaching faults are oblique-normal or pure normal types. Their strike, dip and the obliquity of their striae change systematically. This occurred in order to accommodate extension across the relay ramp. Low-angle connecting faults occur at a high angle to the main fault, and form preferentially when the striae approach the orientation of the strike of the main fault. Slip vectors on the main and secondary connecting fault planes are subparallel, so defining a coherently moving hanging wall. A stress-inversion method was applied for the main fault segments, which characterize a state of stress of regional significance. Calculations were performed for the whole data-sets, including data for the guided connecting faults of the transtensional relay ramps, even though, in theory, stress inversion is not realistic for faults with a guided slip. Indeed, calculations gave a state of stress that is differs from that of the regional stress state. The results should be a warning to geologists that fault geometry has to be clarified in overstepping fault arrays before using the data-set for fault-slip inversion.